The annual estimated costs of termite damage and control in the United States increased from $100 million in 1967 to $1.02 billion in 1986. Among the 30 species of termites reported to be of economic importance in the U.S., five species are considered to have the most significant impact, partly because of their wide distribution. These species include the drywood, or powderpost, termites Cryptotermes brevis, in the southeastern U.S. and Hawaii, and Incisitermes minor, which is found in Texas, the southwest, and in the Rocky Mountains and westward. The remaining three species are the subterranean termites Coptotermes formosanus, in the southeast and Hawaii, Reticulitermes hesperus in the northwest and California, and R.flavipes throughout the U.S. east of the Rocky Mountains. In addition to the termites listed above, other species may cause significant damage in more localized areas.
Subterranean termites most often enter structures from the surrounding soil to feed on wood, or other cellulosic material, of the structure and its contents. Subterranean termites construct an extensive foraging gallery beneath the soil surface. A single colony may contain several million termites with foraging territory extending up to 300 feet (Su, N.Y., R. H. Scheffrahn [1988] Sociobiol. 14(2):353-359). Since subterranean termites are cryptic creatures, their presence is not normally known until after some damage, foraging tubes, or live termites such as swarmers, are found. Some subterranean termites are known to forage beneath an object on the soil surface (Ettershank,G., J. A. Ettershank, W. G. Whitford [1980] Environ. Entomol. 9:645-648).
Control methods for structural infestations of termites varies with the ecology of the different species. Currently, there are two basic approaches for the control of subterranean termites: preventive control and remedial control. In general, preventive measures include the use of wood treated with various repellant chemicals; metal shields between the foundation supports and buildings that either act as barriers, or as a detection method when termites construct visible tubes around the shields; and the creation of chemical barriers by treating the soil under the building foundation, before and after construction, with long-residual termiticides. A layer of basaltic rock particles placed under foundations has been used as a physical barrier to stop the penetration of subterranean termite tunneling. Removal of lumber scraps and sites that accumulate water also discourage the establishment of termite colonies.
Remedial control methods can entail removal of infested wood and replacement with treated wood; drilling and injecting insecticides into small, localized infestations; fumigation of structures with widespread infestations; and use of slow-acting insecticides (Su, N.-Y., M. Tamashiro, and M. l. Haverty (1987) J. Econ Entomol. 80:1-4). Aerial colonies of C.formosanus can be eliminated by the removal of their moisture source. Post-construction soil application of termiticides to eliminate subterranean termite colonies, while commonly attempted, is of limited success (Su, N.-Y., and R. H. Scheffrahn (1990a) J. Econ. Entomol. 83:1918-1924).
In some of the United States, it is mandatory that the soil underlying the foundation of newly constructed buildings be pre-treated with a termiticide to prevent termite infestation. Pesticide is typically sprayed over and into the soil prior to construction. This pre-construction treatment produces a horizontal barrier beneath the building. Because of the lack of communication between pesticide applicator and construction workers, the barrier often loses its continuity during the construction. Moreover, the currently available soil termiticides tend to lose their biological activity after five or more years to the extent that the treated soil is no longer effective against termite invasion. Established termite colonies in the soil may then invade the structure if additional chemical is not applied beneath and around the structure.
When a house or other building is infested by subterranean termites, efforts are made to create a continuous barrier beneath the building in the soil where the subterranean termites are provided access to the building. A common method of creating this barrier is to introduce termiticide around a building foundation by injection into soil underlying concrete foundations, drenching the soil surrounding the building perimeter, or a combination of both. This type of post-construction treatment is labor-intensive and may not adequately produce a continuous barrier (Frishman, A. M., B. L. Bret [1991] Pest Control 59(8):48, 52, 54, 56; Frishman, A. M., A. St. Cyr [1988] Pest Control Technology 16(4):33, 34, 36).
Other remedial treatments include spot treatments such as dusting or injecting termiticides within the walls of the building. Robert Verkerk has described arsenic trioxide dust treatment using termite lures (Verkerk, R. [1990] Building Out Termites, Pluto Press Australia Limited, P.O. Box 199, Leichhardt, NSW 2040). Verkerk describes the use of stakes or blocks of termite susceptible timber to lure termites after the stakes or blocks have been placed near a known termite problem. Once termite activity is observed, arsenic trioxide is injected. Alternatively, a portion of the termites may be dusted with arsenic trioxide.
The effectiveness of the former standard soil termiticides, chlordane and heptachlor, precluded substantial research in alternative termite control methods. Since their withdrawal from the market in 1987, replacement termiticides include chlorpyrifos (Dursban TC) and isofenphos (Pryfon 6), cypermethrin (Demon TC), permethrin (Dragnet FT), fenvalerate (Tribute) and imidacloprid(Premise). Given the loss of chlordane and heptachlor, alternative control measures, such as the use of toxicant and insect growth regulator baits, are being researched (Su, N.-Y., and R. H. Scheffrahn (1990b) Sociology 17:313-328).
A wide variety of termite control methods have been proposed. Japanese patent applicationNos. 61-198392 and 63-151033 describe wooden vessels specifically designed to "attract" termites as part of a monitoring procedure. In the 63-151033 application, the termites are further exposed to a toxicant which is then presumably carried back to the nest in hopes of killing the queen via trophallaxis or food exchange.
Australian Patent No. 1,597,293 (the '293 patent) and a corresponding Great Britain Patent, No. 1,561,901, describe a method which involves mixing insecticide with a food matrix comprising cellulose and a binding agent.
One termite control method comprises placing a highly toxic material, such as an arsenic-containing dust, at a site of infestation in the hope that this will directly control an effective number of termites at the site and also other termites back in the colony.
Elaborate schemes of pipes to convey liquid termiticides under and surrounding buildings have also been proposed for termite control. It has been suggested that these liquid termiticides may be dispensed into the soil surrounding and below the building through these pipes to provide a continuous barrier to the incursion of termites. This method requires a large quantity of termiticides in order to saturate the soil surrounding the building.
U.S. Pat. No. 5,027,546 describes a system intended for use on above ground termites, i.e., drywood termites, which controls termites by freezing with liquid nitrogen. U.S. Pat. No. 4,043,073 describes a method which attempts to circumvent the problem of repeated application of pesticide. The described method functions by "encapsulating" the insecticide, thus making it more persistent. The overt use of pesticides and their persistence in the environment are not remedied by this system. Another proposed system which fails to alleviate the problem of transferring insecticide directly into the soil is U.S. Pat. No. 3,624,953. This method employs a reservoir of insecticide wherein the vapors of the insecticide are permitted to permeate the soil surrounding the reservoir. Thus, exposure of the environment with toxic substances is not avoided by using this method.
Toxicants which have less environmental effect and which show activity against termites are known (Su, N.Y., M. Tamashiro, M. Haverty [1987] J. Econ. Entomol. 80:1-4; Su, N.Y., R. H. Scheffrahn [1988] Florida Entomologist 71(1):73-78; Su, N.Y., R. H. Scheffrahn [1989] J. Econ. Entomol. 82(4):1125-1129; Su, N.Y., R. H. Scheffrahn [1990b] Sociobiol 17(2):313-328; Su, N.Y. [1991] Sociobiol. 19(1):211-220; Su, N.Y., R. H. Scheffrahn [1991] J. Econ. Entomol. 84(1):170-175; Jones, S. [1984] J. Econ. Entomol. 77:1086-1091; Paton,R., L. R. Miller [1980] "Control of Mastotermes darwiniensis Froggatt (Isoptera: Mastotermitidae) with Mirex Baits," Australian Forest Research 10:249-258; McHenry, W. E., U.S. Pat. No. 4,626,528; Henrick, C. A., U.S. Pat. No. 5,151,443).
It should be noted that attractants other than water for termites have been investigated. For example, the extract from brown-rot fungi chemically resembles the trail-following pheromones of termites. Natural pheromones, however, are species- and even colony-specific. A pheromone that is "attractive" to one species or colony of termites may repel termites of other species or colonies. It is of uncertain value, therefore, to incorporate pheromone mimics (such as the brown-rot fungi extract) in a bait, especially if a bait is to be used against a wide range of termite species.
Reported natural enemies of termites consist of general predators such as birds, lizards, spiders, ants, and centipedes. Parasitic mites are known to parasitize termites in laboratory colonies. Phorid and calliphorid flies have been reported as parasitoids of African and southeast Asian termites. Insect parasitoids of North American termites have not been recorded. Nematodes have been found in termites, and a few species have been evaluated as potential control agents. However field efficacy by these nematodes was not adequate.
Several microbial pathogens have been isolated from termites (Sands, W. A. (1969) "The association of termites and fungi, pp. 495-524, In K. Krishna & M. F. Weesner [eds.] Biology of Termites Vol.I, Academic Press, New York; Beal, R. H. and A. G. Kais (1962) J. Invert. Path. 4:488-489; Kimbrough, J. W. and B. L. Thome (1982) Mycologia 74:201-209. Bioassays of Metarhiziumanisopliae (Hanel, H. (1982) Z. ang. Ent. 94:237-245; Lai, P. Y., M. Tarnashiro, J. K. Fujii (1982) J. Invert Path. 39:1-5; Fernandes, P. C. (1991) Microbial control of Cornitermes cumulans (Kollar, 1832) (Isoptera-Termitidae) with Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metsch.) Sorok., Ph.D. dissertation. Univ. Sao Paulo, Piracicaba, 114 p.; Beauveria bassiana (Lai et aL (1982) supra; Fernandes (1991) supra; Gliocladium virens (Kramm, K. R., D. F. West (1982)J. Invert. Path. 40:7-11; species of Entomophthora (Yendol, W. G. and J. D Paschke (1965)J. Invert. Path. 7:414-422; Hanel(1982) supra, and Bacillus thuringiensis (Smythe, R. V. and H. C. Coppel (1965) J. Invert. Pathol. 7:423-426) have all shown that termite mortality can occur under laboratory conditions. A field application of M. anisopliae resulted in recoveries of infected termites, but it did not eliminate the colonies (Hanel and Watson 1983). While potential for microbial control is evident in the laboratory, efficacy under field conditions has generally been lacking. A United States patent has been granted for a fungus showing high activity against fire ants, U.S. Pat. No. 4,925,663. This isolate, designated Beauveria bassiana isolate No. 447, was deposited in a public repository. This isolate is also active against cockroaches (WO 95/25430). The subject invention concerns the new use of B. bassiana No. 447 for control of termites.